1. Field of the Invention
This invention generally relates to an evaporation control apparatus for an internal combustion engine. More specifically, the present invention relates to an evaporation control apparatus that prevents fuel vapors within a fuel tank from escaping to the atmosphere.
2. Background Information
There has been known an evaporation control apparatus that is provided with a fuel tank, a canister disposed outside the fuel tank, and a control valve disposed on an evaporation passage that connects the fuel tank and the canister. The canister temporarily stores fuel vapor from the fuel tank. Such an evaporation control apparatus is disclosed in Japanese Laid-open Utility Model Application No. 2541778. A diaphragm control valve has been used conventionally as a control valve in an evaporation control apparatus.
Recently, there has also been considered an evaporation control apparatus in which a large canister is disposed within a fuel tank in order to increase the efficiency with which the canister adsorbs the fuel vapor. Such an evaporation control apparatus is disclosed in Japanese Laid-Open Patent Publication 64-00347. In this arrangement, the control valve is still positioned outside the fuel tank. The case body of the canister and the diaphragm of this kind of control valve are generally made of a resin material. In recent years, it has been found that fuel components such as hydrocarbons may permeate in very small quantities into the resin materials that form the case body of the canister and the diaphragm of the control valve.
In the conventional arrangement, a control valve is provided in an evaporation passage, which is provided outside the fuel tank to connect the fuel tank to the canister. Therefore, as the pressure rises inside the fuel tank and causes the pressure in the evaporation passage to exceed the atmospheric pressure, fuel vapor may permeate and escape from hoses, joints, and other parts that are connected to the control valve. Similarly, when highly concentrated fuel vapor fills the control valve, the pressure within the control valve exceeds the atmospheric pressure. As a result, the fuel vapor may permeate the case body of the canister and the diaphragm of the control valve. Therefore, fuel components contained in the fuel vapor may escape in very small quantities, into the atmosphere from the control valve.
In order to prevent such undesirable dispersion of fuel components, it is possible to make the case body of the canister and the diaphragm of the control valve out of resin materials that are resistant to the permeation and penetration of fuel components. However, such a solution would increase the cost of the evaporation control apparatus.
Particularly in recent years, concern for the environment has resulted in increasingly stringent demands for reducing emissions of fuel vapors and fuel components into the atmosphere. It is therefore necessary to take comprehensive measures to prevent dispersion of these fuel components, even though the amount of dispersion is small.
In view of the above, there exists a need for an evaporation control apparatus which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
Accordingly, an object of the present invention is to provide an evaporation control apparatus that reliably suppresses the emission of fuel components into the atmosphere.
The forgoing object of the present invention can be attained by providing an evaporation control apparatus adapted to be arranged in a fuel tank of an internal combustion engine and coupled to a suction system of the internal combustion engine. The evaporation control apparatus comprises a canister and a control valve. The canister contains an adsorbent that temporarily adsorbs fuel vapor generated within the fuel tank of the internal combustion engine. The control valve is fluidly coupled to the canister to supply fuel vapor from the fuel tank to the canister when pressure within the fuel tank exceeds a prescribed pressure. The canister and the control valve are configured as a unit to be disposed within the fuel tank.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.